GA4 Sessions vs. Universal Analytics Sessions

Learn how GA data collection, settings & user interactions with your site can affect session metrics. These 8 factors can explain higher/lower session numbers.

comparing sessions in GA4 to sessions in Universal Analytics
Jan 9, 2023
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This article was inspired by a client question:

We’ve been working on moving our websites from UA to GA4 for Google Analytics, and I’ve noticed a significant difference in “Sessions” between the two. We do a report for our company executives about website traffic and have always used Sessions as the metric to report. Is reporting Sessions the best way to communicate traffic or is a different metric better?

There was also a follow-up to this question asking why the session count is different between GA4 and UA. These types of questions are only going to get more common as more websites start using GA4 alongside Universal Analytics. 

Even though sessions are not exactly the same between UA & GA4, Sessions is still the best metric to monitor trends in website traffic. But you should know how sessions are measured differently in GA4 vs. UA, and various factors that can affect the number of sessions reported.

Comparing session count: GA4 vs UA

Session count between the two platforms is not likely to match, since sessions are calculated differently in each (more on that below). Your session count might be higher or lower in GA4 depending on:

  • How users interact with your website (and app if you have one)
  • How your analytics properties are set up

<div class="post-note">When comparing metrics in GA4 & UA, make sure you’re looking at the same date range and user segment in both platforms. It’s also a good idea to double check that all your tags are firing correctly in both.</div>

1. Why UA sessions can be higher than GA4 

  • UA starts a new session at midnight
  • UA starts a new session if the user encounters a UTM parameter

2. Why GA4 sessions can be higher than UA 

  • GA4 has a longer time window for processing late hits
  • GA4 can count engaged sessions without a pageview
  • GA4 automatically uploads logged iOS events when the app is backgrounded

3. Factors that can affect session count either way

  • Session timeout settings in GA4 & UA may not be the same
  • Data filters in GA4 & UA may not be the same
  • GA4 estimates session count 

A closer look at each factor in GA4 vs UA

Here’s more detail about each of the factors that can cause different session counts in GA4 and UA:

1. Time zones of website users 

UA starts a new session at midnight, based on the time zone set for your website in Google Analytics. GA4 doesn't start a new session at midnight. So visitors who are on your website at midnight will restart a session in UA but not in GA4.

Effect: This could make session count appear higher in UA.

2. Session timeout settings

The default session timeout is set to 30 minutes in both GA4 & UA, but it can be adjusted.

Effect: If the session timeout settings don’t match, that would make the session count different.

  • UA min/max session timeouts: 1 minute / 4 hours
  • GA4 min/max session timeouts: 5 minutes / 7 hours 55 minutes

How to adjust UA session timeout settings

<div class="post-action">Click Admin, find the Property column, click Tracking Info, then click Session Settings.</div>

Universal Analytics screenshot showing where to find session settings

<div class="post-action">Adjust the Session timeout to the desired time interval and click Apply.</div>

How to adjust GA4 session timeout settings

<div class="post-action">Click Admin, find the Property column, click Data Streams, then click on your Web stream.</div>

GA4 screenshot showing where to find the web stream

<div class="post-action">Scroll down and click Configure tag settings.</div> 

Configure tag settings in GA4

<div class="post-action">In the Settings panel on the next screen, click Show all. Scroll down and click Adjust session timeout.</div>

adjust session timeout in GA4

Adjust the Session timeout to the desired time interval and click Save in the upper right.

3. Timing of "hits" in GA4 vs UA

Hit timing is different from session timeout. Each individual user interaction with a website is called a hit: pageviews, transactions, events and more (and in GA4, every hit is an event). Data processing latency is 24-48 hours. Sometimes website hits aren’t processed in a timely fashion because of implementation or network constraints.

This Analytics Help page details how late hits are counted differently in GA4 and UA.[1] Here’s a summary:

  • UA: Late hits are processed if they arrive within 4 hours of the end of the day.
  • GA4: Late hits are processed if they arrive within 72 hours of the end of the day.

Effect: GA4 processes hits (events) across a broader time range which may lead to a higher session count.

This Analytics Help page offers more insight into the data limits for UA properties.[2]

4. GA4 reports "engaged sessions"

In GA4 an engaged session is one that lasts longer than 10 seconds (you can adjust this default time if you wish), or has at least 2 pageviews, or has at least 1 conversion event.

<div class="post-note-cute">Engaged sessions in GA4 are an improvement on the Bounce rate metric in UA. Example: a user lands on a page, reads all of the content and is satisfied with the answer. After two minutes they leave the website (without clicking on anything). That counts as an engaged session in GA4, but would count as a “bounce” in UA, even though your page was the one that fulfilled their query.</div>

GA4 automatically detects user activity (like scrolling down a page) and UA doesn’t. So in GA4, an engaged session can begin without a pageview. But in UA a session has to start with a pageview.

Example: a user visits a page of your site and quickly leaves (but the browser tab is still open). After 30 minutes or more (long enough for the session to time out) the user comes back and reads all the content on your web page.

In UA this would be counted as a single session with one pageview, because there was no detectable new pageview or user activity. In GA4 this would be counted as two sessions: one regular session (with a pageview event) and one engaged session (because it lasted longer than 10 seconds).

Effect: Because GA4 can measure engaged sessions based on user behavior other than a pageview, the session count can be higher.

5. UTM parameters

GA4 does not restart session count if a user encounters new campaign parameters while on the site, but UA does. 

  • Example one: you have UTM parameters on some internal links to track which elements get the most clicks. If so, a site visitor who clicks a UTM-tagged internal link will start a new session in UA but not in GA4.
  • Example two: a user was on the site, left to check their email (perhaps to get a promo code or find a product number), then re-entered the site via an email link with UTM tracking. This would count as 2 sessions in UA but only 1 session in GA4.

The second scenario could also take place if the user left and reentered the site via a Google Ad or a link on a referring site with UTM parameters.

Effect: Site visitor engagement with UTM parameters may increase session count in UA.

6. Session estimation

GA4 uses a statistical estimate of the number of sessions, but UA does not. However, UA does sample sessions when datasets get large.

<div class="post-note-cute">Sampling means looking at a small subset of data to infer information about a larger data set. Google gives this example: if you want to count the number of trees in a 100-acre forest, count the trees in one acre and multiple by 100. Learn more about data sampling in analytics.[3]</div>

Effect: Differences in how session metrics are calculated can lead to different session counts between UA & GA4.

7. Filters

Because you can create custom filters in UA, certain reporting views may be filtered to exclude some data—which can affect the number of sessions reported. 

GA4 doesn’t have reporting views. GA4 applies filters at the property level, and currently offers only two types of filters: include/exclude internal traffic, or include/exclude developer traffic.

Effect: If UA & GA4 properties have different data filters in place, this can affect session count.

8. iOS app events are counted differently

GA4 and UA count metrics differently when a user moves an iOS app (including browser apps) to the background.

GA4 events (including session_start) are automatically uploaded when an iOS app is backgrounded, but this doesn’t happen in UA.

Effect: Sessions from iOS apps can be a lot higher in GA4.

Bonus: GA4 session calculation update

If you were an early adopter, your session counts within GA4 may be different for data collected before and after October 2021 because that’s when Google updated the session metric calculation method.[4]

Bottom line: Keep the focus on business goals

Sessions are a good way to benchmark total website/app traffic and monitor traffic trends from a high level, but racking up a higher session count shouldn’t be an SEO objective in and of itself. Here’s what matters more:

  • Is your website attracting increased organic traffic from qualified users?
  • Are users finding value in the content on your website?
  • Are website users performing meaningful actions (aka conversion events) on your site?
  • Are the conversions on your website leading to increased business revenue?

Two things you can do today to improve GA insights

  1. If you haven't setup GA4 yet, you should do so ASAP so you can verify that any GA4 vs UA reporting discrepancies are tracking related, not performance related.
  2. For any organic search reporting, it's smart to include data from Google Search Console and Bing Webmaster Tools to verify long-term trends—this will be even more important after UA sunsets.

Momentic creates, tests, and iterates results-driven SEO strategies for brands in nearly every industry vertical. If you’d like to know more about creating, implementing or tracking the results of an effective SEO strategy, book a free consultation. We do one-time projects as well as ongoing work, and we’d love to help your website reach its full potential!

<div class="post-note-cute">If you need help with GA4 implementation, reporting audits, dashboard configuration, or if you have questions about anything analytics related, don't hesitate to reach out: info@momenticmarketing.com</div>

Resources mentioned in this article

  1. [UA→GA4] Universal Analytics versus Google Analytics 4 data (support.google.com)
  2. Data limits for Universal Analytics properties (support.google.com)
  3. About data sampling - Analytics Help (support.google.com)
  4. [GA4] About Analytics sessions (support.google.com)

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